The specific goal is to provide a better understanding of tryptophan and lysine catabolism and of regulatory interactions of their pathways that may be important in normal and pathological functions in mammals. Our previous work has provided evidence that kynurenine aminotransferase, alpha-aminoadipate aminotransferase, and halogenated tyrosine aminotransferase are identical. We are investigating various implications of these identities relating to regulatory functions in the several metabolic pathways in which these enzyme activities may function. We will also attempt in studies of cellular organelles, whole cells, and whole animals to determine whether the several intracellular localizations of the degradative enzymes may result in permeability barriers that may regulate the pathways. An effect of Ca ion on kynurenine aminotransferase of isolated mitochondria is being investigated as a possible regulatory factor in tryptophan (and lysine, hydroxylysine, and thyroid hormone) metabolism. We expect the studies to reveal new aspects of metabolic regulation of wide application.